I, too, lost my 1st battery early (though not within a day). I now make it a habit to turn everything off (radio, heater/ac, lights) before turning off the ignition. Now I've only changed the battery at my normal 4-5 yr interval. It does draw a lot of juice as the computer is always on and even the cigarette lighters are with power when the ignition is off (which means you can charge your phone over night or at the movies)

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Mark _______________________________
2001 X5 4.4i topaz blue/sand Sport, complete Dinan S2 , hitch, V1, tint, BSW Stage 1, Alpine INA-W910BT
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Life is not fair!
You can't protect people from their own stupidity!
Laughter makes life worth living